1. Field of the Invention
The present invention relates to electronic mapping technology. More specifically, the present invention relates to systems and methods for utilizing an electronic compass or a GPS directional fix to orient a map in the display of an electronic device so as to be consistent with the orientation of the device with respect to Earth.
2. Description of the Related Art
The use of computer mapping technology has been growing dramatically in recent years. The widespread availability of accurate electronic maps and the low cost of processing and display technology have been driving forces behind this trend. Maps are available on fixed media, within memory, and over networks, such as the Internet. Mapping software systems with GPS based position determination are now deployed in motor vehicles such that localized maps are readily available to users. An example of this implementation is in rental cars where detailed maps and driving directions are provided to the user in a mobile mapping device installed in the rental car.
In the GPS implementation, a present location point is displayed on the map, based on a GPS position fix, such that the user""s location is plotted on the map as they move from place to place. The orientation of the user""s movement can be determined by calculating the general direction of movement from position fix to position fix. However, since the resolution accuracy of the GPS system is limited, a small amount of movement cannot be reliably determined, and thus orientation cannot be accurately calculated.
Traditionally, the orientation of a map has been with north at the top. The user is left to abstract this orientation to the physical world. As mapping technology has become more readily available and more responsive to a user""s particular environment, this orientation tradition has become limiting. For example, in a hand-held portable device where the map is displayed with a pointer to the user""s present location, the user has a tightly interactive relationship with the map and the physical environment. The user studies the map and then views the physical environment to locate and track their position and destination. When the map is always displayed with north on the top, it does not reflect the user""s actual view of the area surrounding them. It is preferable in such situations that the map be reoriented to display on top, what is directly in front of the users. Thus, the intimate interactive relationship is improved and the map more readily beneficial to the user.
While the foregoing reorientation of a map display can be accomplished with GPS based systems, the positioning accuracy limitations of the GPS system causes problems. When a mapping device is turned on, there can be no immediate orientation because the GPS approach requires two successive position fixes in order to determine a heading fix. In addition, there must be sufficient movement to overcome the inherent measurement inaccuracies of the GPS systems. Also, when the device motion slows to the point where the movement between successive fixes is less than the resolution of the GPS system, then a degree of uncertainty arises as to what the current orientation, or heading is.
Thus there is a need in the art for a method and apparatus for orienting a map display in a mobile or portable device.
The need in the art is addressed by the apparatus and methods of the present invention. The inventive apparatus is a mobile device with a map memory and a compass operable to output compass headings. A controller is coupled to the memory and operates to recall a map therefrom. The controller is also coupled to the compass and is operable to read a compass heading therefrom. A display is also coupled to the controller. The controller calculates an offset value indicative of the difference between the compass heading and the orientation of the map and writes the map to the display in accordance with the offset value.
In a further refinement, the controller repeats the calculation of the offset value and rewrites the map to the display in accordance therewith. The controller repeats this periodically. In a further refinement, the controller repeats when the offset value indicative of the difference between the compass heading and the orientation of the map exceeds a threshold value.
In another embodiment of the present invention, the mobile device comprises a map memory, a GPS receiver operable to output position fixes, and a compass operable to output compass headings. A controller is coupled to the memory and operable to recall a map therefrom, and the controller is coupled to the GPS receiver and operable to calculate a heading fix based on a first and a second position fix read therefrom. The controller is also coupled to the compass and operable to read a compass heading therefrom. A display is also coupled to the controller. The controller calculates a map offset value indicative of the difference between the heading fix and the orientation of the map. However, if the heading fix is unavailable, the controller calculates an offset value indicative of the difference between the compass heading and the orientation of the map. Finally, the controller writes the map to the display in accordance with the offset value, however determined.
In a refinement of the foregoing embodiment, the controller repeats the calculation of the offset value and rewrites the map to the display in accordance therewith. Further, the controller repeats this periodically. In a further refinement, the controller repeats when the second GPS position fix is offset from said first GPS position fix by at least a threshold value. In another refinement, the controller repeats when the offset value indicative of the difference between the compass heading and the orientation of the map exceeds a threshold value.
The present invention also teaches several methods of operation. These include a method of orienting a map display in a mobile device including the steps of reading a compass heading indicative of the orientation of the mobile device and calculating an offset value indicative of the difference between the compass heading and the orientation of a map. Then, writing the map to a display in accordance with the offset value.
A refinement of this method includes the additional step of updating the map orientation by repeating the reading, calculating and writing steps. In a further refinement, the updating step is repeated periodically. In a further refinement, the writing step is executed when the offset value indicative of the difference between the compass heading and the orientation of a map exceeds a threshold value.
Another method of orienting a map in a mobile device display includes the steps of reading a first and a second GPS location fix and calculating a GPS heading fix indicative of the direction of motion of the mobile device. Upon determining that a GPS heading fix is unavailable or indeterminate due to accuracy or other reasons, the invention includes the step of reading a compass heading indicative of the orientation of the mobile device. Then, the inventive method calculates an offset value indicative of the difference between the GPS heading fix and the orientation of a map. If this is not available or is indeterminate due to accuracy or other reasons, the inventive method otherwise calculates an offset value indicative of the difference between the compass heading and the orientation of a map. Finally, the method writes the map to a display in accordance with the offset value.
A refinement of this method is to update the map orientation by repeating the reading, calculating and writing steps. In a further refinement, the updating step is repeated periodically. In a further refinement, the updating step is repeated when the second GPS position fix is offset from the first GPS position fix by at least a threshold value. In another refinement, the writing step is executed when the offset value indicative of the difference between the compass heading and the orientation of a map exceeds a threshold value.